Builders,
In the previous story, The small world of Experimental Aviation , I mentioned how much N-1777W changed over the years. He is a look at some of it:
.
.
This is the plane at Oshkosh 1970. The picture made it to the back cover of Sport Aviation in January 1971. Notice it once had 140HP heads, and other well meaning, but weak ideas. If you have the Tony Bingelis book “Firewall Forward” the Pietenpol/Corvair pictures in it are all of this plane, in this era. Bingelis didn’t like auto engines, and his writing spread a lot of old wives tales. He was a good guy and a highly influential writer, but he held opinions that testing by his contemporaries like Wittman and Monnett showed to be wrong.
.
.
Fast forward to 1995. Want to know how I became the expert on Pietenpol weight and balance? Want to know why I think it is annoying when people who can’t do a simple calculation, or have never weighed a plane on electronic scales question my work on Piet W&B? Start with this photo: The reason why the cowl has a 6″ wide expansion in it is simple. After getting the plane, I found out the weight and balance, done on bathroom scales was dangerously wrong. I carefully measured, and in a single day, made a mount 6″ longer and plugged the cowl for test flying. In the picture is Gus Warren who did a lot of the work with me and covered much of the flying. It was an instant improvement in safe flying behavior. I have written extensively about this testing and work, you can find the links here: Corvair – Pietenpol Reference page, but today, the majority of Pietenpol builders willfully ignore the information. Much of this is driven by people in the Pietenpol community who personally dislike me for my tone or experience.
.
.
Above, same plane 1999. This is an entirely different motor mount, the first high thrust line (#4201-C Pietenpol Motor mounts, now on the shelf, ready for shipping.) and a completely different set of gear legs.(New die spring landing gear on a Pietenpol, 10 a.m.-4 p.m.) Bring up the topic of axle location, gear leg length, CG changes or thrust lines, and people will tell you they think it makes no difference. Of course their opinion is not based on any testing, just a guess, something they heard from a guy. When I speak of these things on a Pietenpol, it was because for a number of years, ready to cut up a good flying plane, or a mount that I had made a month before, in search of something better. Some opinions are made of guesses, mine are made of testing.
.
If you look in the upper corner of the picture, there is a blond girl sitting in the grass. She was getting away from her job as a newspaper editor. She liked planes a lot, and had a very pleasant way about her. Her name turned out to be Grace.
.
Above, side view of the same plane, taken just before Corvair College #1. Notice how much longer the gear is than when the fuselage was orange. Also note where the axle is located. In the last few years, we have had two Corvair powered Pietenpols heavily damaged by being put on their back, even though I warned people to move the axle forward if using brakes. It is frustrating to not be able to motivate people to correct things like this before an accident. When you see what I was willing to rework on my own aircraft to make it better, it is obvious that I don’t operate things in a condition that simple work and modest money will fix. If you are too tired to improve things, pick a different hobby, this one has potentially harsh penalties for the lazy.
.
-ww.
.
Just stop and think how many years ago that aircraft was designed, only a fool would think that there have not been any worthwhile design improvements put forward over the years. If they are truly improvements then they would have been proven out by actual aircraft experience over time. Improved gear design is a very simple example and this article is clear indication that the original plans are just a starting point for the builder. As an engineer I see everything as improvable however some improvements just are not worth the effort. I just can’t think of why a builder would not want to look at the work that has been done to examine such an old design and address issues that have been discovered as well as improvements that have been found to be worthwhile. The article mentions adding brakes which apparently were not original to the design even though they seem like a must have so why not shift the gear to avoid an easy nose over while you are at it. The EAB class is for Education and Recreation so why not try getting educated before you start building.
Sarah, what is interesting about the development of Pietenpols is this: not much happened on the drain from 1941-60. At that point Bernard Pietenpol got excited about the Corvair, and after he flew it on a J-3, he started a whole second era of Piets lasting 1960- the end of the 70s. This saw the Corvair work, long fuselages, 3 piece wings, and revised w&b data. Much of this data was readily available from Bernard’s son Don, but because it was labeled ‘Corvair info’ many Piet builders who didn’t want to use a Corvair ( nor spend a whopping $20 ) ever read it. The prime example is the 1930s plans have the axle 10″ behind the LE, but the Corvair plans, made for an era with brakes have the axle just half an inch from the LE. Bernard in the second era, evolved his own design, but for some reason many builders want to pretend BHP s only work was pre WWII .
“made for an era with brakes have the axle just half an inch from the LE.” Not design advice and don’t try this at home. But many of us who get a kick out of aircraft design see things. Poor-Man’s area Rule of aligning bodies and for other reasons ( such as brakes ) has a lot of homebuilts with their mains darn close to what you did on your Piet, aka the axle vertical centerline is real close if not spot on with the leading edge. Look at a photo or side view drawing of a Tailwind, Panther, RV series, and so many more. Perhaps you are in good company here William…
BHP, knew all this. In 1930, airfields were square and grass, and you always landed into the wind, that is why tail skids and no brakes were ok. To turn a plane with a tail skid, you push the stick forward and apply power, that is why the gear was 10″ aft in 1929. Once you have brakes, and you are going to land on pavement or with cross winds, it has to be much further forward like BHP showed in his 1960 drawings.
What are the principles for locating the wheels on a tail dragger? I am building a ch750 and may eventually want to install conventional gear (would like to get rid of the training wheel, and stop people from snickering at me). Simply locating the wheels forward doesn’t address the stability problems, does it? What effect does the location have on preventing ground loops, etc, not just preventing nose overs? I seem to recall such analysis but just now can’t recall where I saw it, looking up in Von Mises, but ultimately would like to hear from an experienced practitioner.
Thanks
Mike
Mike, read Chris Heintz’s book “Your own Wings” to understand why a 750 should never be a tail wheel plane, it is optimized as a tri gear. For landing gear info, Pazmany’s book LG for light AC is at the EAA book store. ww